Classification of stacking faults and dislocations observed in nonpolar a-plane GaN epilayers using transmission electron microscopy

In this study, we presented comparative discrimination methods to identify various line and planar defects observed in nonpolar a-GaN epilayers on r-sapphire substrates. Unlike the case of conventional c-GaN, which is dominated by perfect threading dislocations, systematic identification of undistinguishable defects using transmission electron microscopy (TEM) is necessary to suppress the propagation of defects in nonpolar GaN epilayers. Cross-sectional TEM images near the [0 0 0 1] zone axis revealed that perfect mixed and pure screw type dislocations are visible, while pure edgeand basal stacking faults (BSFs) are not discernible. In tilted cross-sectional TEM images along the image zone axis, the dominant defects were BSFs and partial dislocations for the image and 0 0 0 2 two-beam images, respectively. From plan-view TEM images taken along the image axis, it was found that the dominant partial and perfect dislocations were Frank–Shockley and mixed dislocations, respectively. Prismatic stacking faults were observed as inclined line contrast near the [0 0 0 1] zone axis and were visible as band contrast in the two-beam images along the image and image zone axes.